Jacques Kallis made an unbeaten 74 and Yusuf Pathan 39 not out, including four successive sixes in an Arul Suppiah over that cost 30, in Kolkata's 161-3.

But Van der Merwe smashed two sixes and nine fours to put Somerset on course.

Somerset came as underdogs - Snell

He fell as they wobbled from 120-2 to 123-4, but Nick Compton saw them home by five wickets with two balls left.

Kallis, who also cleared the ropes four times and hit four fours too, batted through the Kolkata innings, but it was Pathan who provided the main fireworks in his assault on Suppiah.

The Malaysia-born slow left-arm spinner, who recorded the best figures in a decade of Twenty20 cricket earlier this season, gained a measure of redemption with 15 from 11 balls before Compton hit the winning boundary.